Conventionally, when making an optical connection between optical fibers, an optical fiber connector (hereinafter referred to as a connector) is attached to each of the ends of the two optical fibers. These two connectors are connected to an adapter so that the end surfaces of the optical fibers abut and form a connection.
This type of connector generally comprises: a housing that is attachable to and removable from an adapter; a ferrule housed in the housing that can move along an axial direction; and a compression coil spring mounted in the housing and biasing the ferrule along the axis toward the free leading end.
A fiber insertion hole (e.g., with a diameter of 127 microns) is formed at the axial center of the ferrule. Cladding portion (e.g., with a diameter of 125 microns) at the end of the optical fiber is inserted through and supported in the fiber insertion hole.
The ferrule and the end surface of the cladding portion in each connector are polished to form a co-planar surface. When the two connectors are connected via the adapter, the end surfaces of the ferrules of the connectors are pressed by the compression coil spring so that the end surfaces of the ferrules abut each other and form a connection. As a result, the end surfaces of the cladding portion are pressed against each other in a stable manner to form a connection.
However, the fiber insertion hole of the ferrule is often formed eccentric relative to the axial center due to production tolerances and the like (e.g., eccentricities of 1 micron or less). Thus, at the connection surface of the optical fibers, there may be a radial offset between the fiber insertion holes of the ferrules. In other words, there can be a radial offset between the cladding portion (i.e., the core (e.g., 9 microns in diameter) formed at the center of the cladding portion) of the two optical fibers inserted into the fiber insertion holes. This leads to optical loss and a reduction in optical transmission rates.
The present applicant has implemented a connector with a ferrule provided with a hexagonal flange and a hexagonal hole formed inside the housing that can engage with a hexagonal flange. In this connector, when the ferrule is housed in the housing, the hexagonal flange engages with the hexagonal hole while being biased by the compression coil spring. Thus, the ferrule cannot rotate relative to the housing.
In this connector, at an assembling and adjusting stage, once the ferrule is housed in the housing, the engagement between the hexagonal flange and the hexagonal hole is released by inserting the tip of a specialized jig from the end of the housing to apply pressure against the biasing force from the compression coil spring. Then, the jig is rotated to rotationally adjust the ferrule relative to the housing, thereby allowing the positioning at one of six positions at which the hexagonal flange and the hexagonal hole can engage. The position that is selected from the six positions is the position at which the radial offset between the fiber insertion holes is minimized. When the tip of the jig is removed from the housing, the hexagonal flange re-engages with the hexagonal hole so that the ferrule cannot rotate relative to the housing.
Japanese Laid-Open Patent Publication Number 8-160255 discloses a connector with a stop ring which is screwed to the inside of the housing. A key on this stop ring slidably engages with a key groove formed on a flange of a ferrule and extending along the axial direction. When assembling this connector, the ferrule and the stop ring can be rotated 360° around the axis in a non-stepping manner relative to the housing. Then, adhesive is injected into the housing so that the housing and the stop ring are secured and the ferrule cannot rotate relative to the housing.
In polarization-retaining optical fibers, the cladding portion is formed with a core and a stress application section (e.g., a quartz glass with additives, which is formed from B2O3). Light is transmitted while a predetermined polarization state is retained. Thus, when connecting together polarization-retaining optical fibers, the polarization-retaining optical fibers and their cladding portions must be connected to transmit light while the polarization state is retained by adjusting the rotational phase.
In the connector implemented by the present applicant, the hexagonal flange of the ferrule is engaged with the hexagonal hole in the housing. This prevents rotation of the ferrule relative to the housing. However, the hexagonal flange and the hexagonal hole can engage only at any one of six positions. As a result, it is difficult to eliminate completely optical loss at the connection surface between the optical fibers, thereby reducing the optical transmission rate.
Also, in this connector, after the ferrule is housed in the housing, the tip of a specialized jig is pushed in from the leading end of the housing to release the engagement of the hexagonal flange and the hexagonal hole. The jig is then rotated to adjust the angle of the ferrule relative to the housing. Since the ferrule cannot be adjusted while observing from the leading end, making the adjustments for the appropriate positioning of the ferrule becomes more difficult.
In the connector of Japanese Laid-Open Patent Publication Number 8-160255, the ferrule that can be rotationally adjusted 360° around its axis relative to the housing in a non-stepping manner. Thus, reduction in the optical transmission rate can be minimized. However, a stop ring is screwed to the inside of the housing, thereby making it not easy to make rotational adjustments by rotating the ferrule and the stop ring relative to the housing.